Light-emitting diodes (LEDs), due to their high luminance and energy efficiency, have been recognized as the third generation lighting source and seen rigorous development in recent years. A GaN-based epitaxial wafer grown on a substrate can be a foundation for typical LEDs and determines their performance.
In general, a LED epitaxial wafer comprises a substrate, an N-type conductive layer, a stress releasing layer, a light emitting layer, an electron blocking layer, a P-type conductive layer and a P-type contact layer, wherein, the structure of the light emitting layer and the quality of the crystal are determinant to the photoelectric properties of the semiconductor device. However, in semiconductor devices based on Group-III nitrides, as the quantum well layer mostly differs from the N-type conductive layer and the quantum barrier layer in terms of materials and components, stress will be generated in the quantum well layer, thus generating polarization charges at the interface between the quantum well and the quantum barrier to form a polarization field. This polarization field will cause quantum Stark effect in the quantum well layer that makes electrons and hole wave functions separated, thus reducing photoelectric conversion efficiency and light emitting efficiency.